PAGE 24
Processing of Heavy Crudes –
Challenges and Opportunities to the
Downstream Industry
Marcio Wagner
Introduction The processing of heavy crudes shows some tech-
nologic challenges to refiners once, due to his
The continuous supply of adequate crude oil to the
lower yield in distillates, it’s necessary the installa-
refining hardware is one of the assumptions adopt-
tion of deep conversion technologies aiming to
ed by the refiners to the installation of refining as-
produce added value streams that meet the cur-
sets or economic analysis of already installed units.
rent quality and environmental requirements, fur-
However, according to the installed geopolitical
thermore the concentration of contaminants like
scenario, the supply of adequate crude oil to the
metals, nitrogen, sulfur, and residual carbon tends
refining hardware can be seriously threatened,
to be high in the heavier crudes, making the pro-
mainly to refiners that operate with lighter and
cessing of his intermediate streams even more
high cost crudes.
challenger.
In this sense, more flexible refining hardware in
Technologic Challenges
relation of the processed crude slate is an im-
portant competitive advantage in the downstream The challenge in the processing of heavy crude oil
sector, mainly the processing of heavy and extra- starts in the desalting step before the sent to the
heavy crudes due to his lower acquisition cost distillation unit. The desalting process consists
when compared with the lighter crude oils. The basically in the water addition to the crude aiming
difference in the acquisition cost between these to promote the salt removal from the oil phase
oils is based on in the yield of high added value that tends to concentrate in the water phase, Fig-
streams which these oils present in the distillation ure 1 presents a simplified process flow diagram
process, once the lighter crudes normally show for a crude oil desalting process with two separa-
higher yields of distillates than the heavier crudes, tion stages.
his market value tends to be higher.
Figure 1 – Crude Oil Desalting Process with two Separation Stages
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The separation of oil and water phases in the sepa- Table 1 – Crude Oil Classification Based on API
ration drums occurs through the sedimentation Grade
process, due to the density gap between the water
and the crude oil. Considering that the sedimenta- Classification API Grade
tion process can be theoretically described by the Light Crude API >31,1
Stokes Law, according to equation 1.
Medium Crude 22, 3 > API < 31,1
Heavy Crude 10,0 > API < 22,3
(1)
Extra-Heavy Crude API < 10,0
According to equation 1, the sedimentation veloci- After the desalting process, the crude oil is sent
ty is proportional the density gap, in the case of to the atmospheric distillation tower, according
heavier crudes, this gap is lower leading to a lower to presented in Figure 2.
sedimentation velocity and the need of higher resi-
dence times to an adequate separation. Another To heavier crudes, the yield of distillates by sim-
complicating factor in the case of heavy crudes is ple distillation is relatively reduced and the bot-
the higher viscosity of the oil phase that hinders tom section in the atmospheric distillation units
the mass transfer in this phase. Due to these fac- tends to be overload. Table 2 presents a compar-
tors, refining hardware designed to process heavy ative analysis of the yields of different crude oils.
crude oils needs more robust desalting sections
taking account the trend of higher salt concentra-
tion in the crude and a harder separation process.
Table 1 presents an example of crude oil classifica-
tion based on the API Grade.
Figure 2 – Atmospheric Distillation Process of Crude Oil
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Table 2 – Estimated Yields in the Atmospheric Distillation Process for Different Crude Oils
Where, VGO = Vacuum Gas Oil
Crude Oil Naphtha Middle Distillate VGO Vacuum Sulfur Specific
Type Yield Yield (wt%) Yield Residue Content Gravity
(wt %) (wt%) (wt%) (wt%)
Brent (oAPI 30,1 25,0 30,3 12,3 0,37 0,8333
38,3)
Bonny Light 27,7 34,1 31,2 5,5 0,14 0,8478
(oAPI 35,4)
Green Canyon
(oAPI 30,1) 16,9 22,6 32,9 26,1 2,00 0,8752
Ratawi (oAPI 15,8 18,0 32,2 32,9 3,90
0,9065
24,6)
Normally, heavy crude oils have higher concentra- Available technologies to processing bottom bar-
tion of metals, sulfur, and nitrogen. These contami- rel streams involve processes that aim to raise the
nants tends to be distributed in the intermediates H/C relation in the molecule, either through re-
streams concentrating in the heavier streams, mak- ducing the carbon quantity (processes based on
ing necessary more robust conversion processes carbon rejection) or through hydrogen addition.
and tolerant to these contaminants. Technologies that involves hydrogen addition en-
compass hydrotreating and hydrocracking pro-
Aiming to avoid damage to the catalysts of deep
cesses while technologies based on carbon rejec-
conversion processes as FCC and hydrocracking,
tion refers to thermal cracking processes like
normally refineries that process heavier crudes
Visbreaking, Delayed Coking and Fluid Coking,
promotes a better fractionating of bottom streams
catalytic cracking processes like Fluid Catalytic
of vacuum distillation tower. When the crude oil
Cracking (FCC) and physical separation processes
presents high metals content, it’s possible to in-
like Solvent Deasphalting units.
clude a withdraw of fraction heavier than the heavy
gasoil called residual gasoil or slop cut, this addi- Due to the high content of contaminants in the
tional cut concentrates the metals in this stream crude oil and consequently in the intermediary
and reduce the residual carbon in the heavy gasoil, chains, refining equipment destined to the pro-
minimizing the deactivation process of the conver- cessing of heavy crudes requires high hydrotreat-
sion processes catalysts as aforementioned. Nor- ment capacity. Usually, the feed streams of deep
mally, the residual gasoil is applied as the diluent to conversion units like FCC and hydrocracking go
produce asphalt or fuel oil. through hydrotreatment processes aiming to re-
duce the sulfur and nitrogen contents as well as
Due to the high asphaltenes content in the heavier
the content of metals. Higher metals and asphal-
crudes, the residual carbon in the bottom barrel
tenes content lead to a quick deactivation of the
streams is also higher than observed in the lighter
catalysts through high coke deposition rate, cata-
crudes, this characteristic reinforces, even more,
lytic matrix degradation by metals like nickel and
the necessity of installation process units with high
vanadium or even by the plugging of catalyst pores
conversion capacity.
produced by the adsorption of metals and high
molecular weight molecules in the catalyst sur-
face. By this reason, according to the content of
asphaltenes and metals in the feed stream are
adopted more versatile technologies aiming to
ensure an adequate operational campaign and an
effective treatment.
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Figure 3 – Reactants and Products Flows in a Generic Porous Catalyst (GONZALEZ, 2003)
Figure 3 presents a scheme of reactants and prod- Available Processing Schemes and Refining
ucts flows involved in a heterogeneous catalytic Technologies
reaction as carried out in the hydroprocessing
Due to the higher severity and robustness of the
treatments.
processes, the installation cost of the refining
In order to carry out the hydroprocessing reac- hardware capable to process heavier crudes tends
tions, it’s necessary the mass transfer of reactants to be higher when compared with the light and
to the catalyst pores, adsorption on the active sites medium oils as well as the operating costs. Figure
to posterior chemical reactions and desorption. In 4 shows a possible refining configuration to be
the case of bottom barrel streams processing, the adopted by refiners to add value to heavy crudes.
high molecular weight and high contaminants con-
The refining scheme presented in Figure 4, nor-
tent require a higher catalyst porosity aiming to
mally called Coking/Hydrocracking configuration,
allow the access of these reactants to the active
is capable of ensuring high conversion capacity,
sites allowing the reactions of hydrodemetalliza-
even with extra-heavy crudes. The presence of
tion, hydrodesulfurization, hydrodenitrogenation,
hydrocracking units gives great flexibility to the
etc. Furthermore, part of the feed stream can be in
refiner, raising the yield of middle distillates. Fig-
the liquid phase, creating additional difficulties to
ure 5 presents a basic process flow diagram for a
the mass transfer due to the lower diffusivity. To
typical hydrocracking unit designed to process
minimize the plugging effect, in fixed bed reactors,
bottom barrel streams.
the first beds are filled with higher porosity solids
without catalytic activity and act as filters to the This configuration is adopted when the contami-
solids present in the feed stream protecting the nants content (especially nitrogen) is high, in this
most active catalyst from the deactivation (guard case, the catalyst deactivation is minimized
beds). through the reduction of NH3 and H2S concen-
tration in the reactors. Among the main hy-
drocracking process technologies available com-
mercially we can quote the process H-Oil™ de-
veloped by Axens Company, the EST™ process
by ENI Company, the Uniflex™ Processes by
UOP, and the LC-Fining™ technology by Chev-
ron Company.
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Figure 4 – Process Arrangement to a Refinery Operating Under Coking/Hydrocracking Configuration
Figure 5 – Typical Hydrocracking Unit Dedicated to Treat Bottom Barrel Streams
PAGE 29
Although the higher processing cost, to process Conclusion
heavy crudes can present high refining margin. As
As briefly described, heavy crude processing of-
described earlier, the reduced acquisition cost in
fers technological challenges to refiners, however,
relation of lighter crudes, as well as the ease of
according to the geopolitical and the downstream
access and reliability of supply, can make the heavy
industry scenarios, processing heavier oils can be
crudes economically attractive, mainly in countries
a competitive advantage. The current scenario of
like Canada, Venezuela, and Mexico that have great
the refining industry indicates a strong tendency
reserves of heavy and extra-heavy crude oils.
to add value through the production of lighter
The flexibility of the refining hardware is a funda- products, mainly petrochemical intermediates.
mental factor to ensure the competitiveness of the This fact, coupled with the need to produce bot-
refiner in the refining market. Normally, the refin- tom streams with lower contaminants after 2020
eries are designed to process a range of crudes, (IMO 2020), increases even more the pressure on
and wider the range, according to the technical refineries with low bottom barrel conversion ca-
limitations, more flexible is the refinery related the pacity under risk of loss of competitiveness in the
processed crude slate, this characteristic is relevant market, in this scenario it is possible to have a
and strategic taking into account the possibility to strong tendency of resumption in the capital in-
enjoy the processing of low-cost crude oils by op- vestments in the preparation of these refiners to
portunity besides giving more resilience to refiner the processing of petroleum residues and heavier
in scenarios of restricting access to the petroleum crudes.
market, mainly face geopolitical crisis.
References
The current scenario of the downstream industry
SPEIGHT, J.G. Heavy and Extra-Heavy Oil Up-
indicates the tendency of reduction in the trans-
grading Technologies. 1st ed. Elsevier Press, 2013.
portation fuels demand and the raising in the de-
mand by petrochemical intermediates creating the ROBINSON, P.R.; HSU, C.S. Handbook of Petro-
necessity of growing the conversion capacity by the leum Technology. 1st ed. Springer, 2017.
refiners in the sense of raising the yield of light ole- GONZALEZ, G. S. Junior Engineer’s Training
fins in the refining hardware. Furthermore, the new Course – Kinetics and Reactors. Oxiteno Compa-
regulation over the marine fuel oil (Bunker), IMO ny, 2003.
2020, should create even more pressure over the
refiners with reduced conversion capacity. GARY, J. H.; HANDWERK, G. E. Petroleum Re-
fining – Technology and Economics.4th ed. Marcel
In a first moment, aiming to comply with the new Dekker., 2001.
bunker specification, noblest streams, normally di-
rected to middle distillates should be applied to Author
produce fuel oil with low sulfur content what
should lead to a shortage of intermediate streams
to produce these derivatives, raising the prices of
these commodities. The market of high sulfur con-
tent fuel oil should strongly be reduced, due to the
higher prices gap when compared with diesel, his
production will be economically unattractive, lead-
ing refiners with low conversion capacity to opt to
carry out larger capital investment in order to give
their refining hardware more robustness for the
processing of heavier crudes. Dr. Marcio Wagner da Silva is Process Engineer and
The market value of the crude oil with higher sul- Project Manager focusing on Crude Oil Refining In-
fur content, normally the heavier crudes, tends to dustry based in São José dos Campos, Brazil. Bache-
reduce after 2020. In this case, refiners with refin- lor in Chemical Engineering from University of
Maringa (UEM), Brazil and PhD. in Chemical Engi-
ing hardware capable to add value to these crudes
neering from University of Campinas (UNICAMP),
can have a great competitive advantage in relation
Brazil. Has extensive experience in research, design
of the other refiners taking into account the lower
and construction to oil and gas industry including
acquisition cost of the crude oil and higher market developing and coordinating projects to operational
value of the derivatives, raising then the refining improvements and debottlenecking to bottom bar-
margins. rel units, moreover Dr. Marcio Wagner have MBA
in Project Management from Federal University of
Rio de Janeiro (UFRJ) and is certified in Business
from Getulio Vargas Foundation (FGV).
